Cboe Global Markets Inc. (CBOE) shares are down 2.9% premarket Friday after it reported its fourth-quarter earnings. Here's what you need to know:

EARNINGS: The exchange operator reported net income of $257.1 million, or $2.26 a share. Excluding the impact of the new tax law and one-time items, the company earned 87 cents a share. Analysts polled by Thomson Reuters had expected adjusted earnings of 88 cents a share.

REVENUE: Net revenue increased 7% to $265.6 million, less than the $267.2 million analysts had expected.

TAX CHARGE: Cboe's results included a $191.5 million benefit stemming from remeasurement of deferred tax positions under the new U.S. tax law.

GUIDANCE: The company said it expects operating expenses to increase 1% to 3% in 2018, and its effective tax rate to be between 26.5% and 28.5%.

VOLATILITY: The earnings report comes two days after the company held a conference call to address concerns about market volatility and its lucrative volatility-related business. Goldman Sachs and JPMorgan both lowered ratings on Cboe shares this week on fears investors might leave these franchises.